Magnetic storage systems, such as hard disk drives, are used to store large amounts of information. A magnetic head in a magnetic storage system typically includes a read/write transducer for retrieving and storing magnetically encoded information on a magnetic recording media, such as a disk.
The ability to increase the storage capacity in magnetic recording is an ongoing concern. As the amount of information to be stored on the magnetic recording media continues to increase, demands for higher-density recording also continue to increase. Perpendicular magnetic recording (PMR), wherein the recorded bits are stored in a perpendicular or out-of-plane orientation in the recording layer, allows for high recording densities in magnetic recording data storage devices such as hard disk drives. The write head must be able to write data not only at high bit densities but also at high data rates.
The switching time for the write pole of the write head to switch from one magnetization direction to the other is a limiting factor as the data rate is increased in PMR. At high data rates, the available magnetic flux from the write head, as seen by the recording layer on the disk, is dominated by the low-frequency flux output of the write head. The reason for such loss of write flux includes a slow intrinsic time-constant of the magnetization reversal in the main pole of the write head. Also, lower data-rate systems require additional overshoot of the write current from the disk drive's write driver circuitry to aid in the magnetization reversal. This additional overshoot requires additional power from the write driver circuitry.
Perpendicular magnetic recording systems with high-frequency assisted writing using a spin-torque oscillator (STO) have been proposed. The STO, which comprises a field-generation layer (FGL) and spin-polarization layer (SPL), is placed within in the write gap. The write head generates a write field that, beneath the main pole, is substantially perpendicular to the magnetic recording layer, and the STO generates a high-frequency auxiliary field to the recording layer. Ideally, the auxiliary field has a frequency close to the resonance frequency of the magnetic grains in the recording layer to facilitate the switching of the magnetization of the grains. As a consequence, the oscillating field of the STO's FGL resonates with the media and provides strong writing despite having a narrow writer.
U.S. patent application Ser. No. 15/140,761, filed Apr. 28, 2016 and hereby incorporated by reference, discloses writers with spin-torque-assisted write field enhancement that use a DC-field-generation (DFG) layer to create an auxiliary magnetic field that adds constructively to the write field and thereby enables high-density magnetic recording. A significant benefit of writers that use a DFG layer is that they enable high-density magnetic recording without requiring resonance with the media. Consequently, there is no need to jointly optimize the writer and the media of the disk drive as there would be to achieve high performance with a writer using an STO.
Regardless of whether a magnetic write head uses an STO or a configuration with a DFG layer as disclosed in U.S. application Ser. No. 15/140,761, there is an ongoing need to improve the performance of the writer.